As known from said prior patent application, each main connecting rod of the revolving dobby is mounted with its idle head on the intermittent-motion drive shaft which drives said dobby to revolve, through a cam which, by being interposed between said shaft and said main connecting rod head, is locked in its position by the action of the thrust tooth of an auxiliary pusher which, by being rotatably hinged onto the fixed body of the revolving dobby, cooperates with either of two radial, mutually opposite notches provided on the periphery of the same cam, or is made integral with said shaft by two swinging, mutually opposite keying levers pivotally installed on said cam and cooperating with each other at one of their ends, wherein a key is present which is urged by two springs to enter one from two, also radial, mutually opposite grooves provided in the drive shaft, with the disengagement of said key from the relevant groove being accomplished thanks to the cooperation of the thrust tooth of a drive pusher, also rotatably hinged onto said fixed body of the revolving dobby, with one of the free ends of said keying levers.
On the other hand, in as much as the need for locking in position the cam, and consequently the relevant main connecting rod, only arises simultaneously with the above said key disengagement, the movements of revolution of said auxiliary and drive pushers are always produced simultaneously through one single cam system.
Such a structure known from the prior art offers considerable advantages, but, unfortunately, is not absolutely free from risks of damaging its own organs under very special circumstances.
In fact, if, owing to an assembling mistake, the cam is not installed in such a way that either of both said locking notches thereof is in correspondence of said tooth of the auxiliary lock pusher so as to be capable of cooperating with it and consequently said tooth of the drive pusher is not in such a position as to be capable of cooperating with the free end of one of both key engagement levers, a subsequent motion of both pusher teeth towards the cam would generate, upon the revolution of the same cam, an interference between said mechanical parts, with consequent breakages.
On the other hand, a possible incomplete operation of key disengagement attained by moving said teeth of both pushers towards the cam in order to lock said cam in its position, leaving the key still partially inside the groove provided along the drive shaft, would keep said cam revolving and the cam, by interfering with the pushers in lowered position, would cause the same drawbacks as said above.
In the same way, an accidental dragging of the cam owing to various reasons, such as foreign bodies entering between adjacent cams, by causing an angular offset in the alignment between the tooth of the auxiliary pusher and the relevant locking notch and consequently between the tooth of the drive pusher and the end of the relevant keying lever, would unavoidably cause fatal sticking events between the above said mechanical organs.
Summing-up, the presence, on the peripheral edge of the cam, of two radial locking notches which must necessarily be provided in corresponding extensions of the same cam, showing more or less vertical walls, can cause, in certain abnormal situations, fatal sticking events to occur between said auxiliary pusher and said drive pusher and said walls of the locking notches.